The invention relates to a method for filling the value preset memory of a franking machine, whose functional sequence is controlled by a central electronic control unit, with a coded information exchange between an authorizing, remote control room and the user of the franking machine. By means of the control unit of the franking machine, an appropriate association between the exchanged information is checked. This invention also relates to a franking machine for performing the method with an electronic control unit having a computer and a memory linked with a plurality of input keys and a display field, one of the memories being a value preset memory for the value quantities to be used by franking.
According to known methods of this type, e.g. according to U.S. Pat. No. 4,097,923, the necessary information forming a pair of numbers authorizing the filling of a value preset memory of a franking machine, are calculated according to a unitary given rule for all the franking machines, i.e. according to an algorithm, both in the control room and in the franking machine. Following an information exchange with the control room, the numbers are compared with respect to possible pair formation in the franking machine. This gives an information pair valid for filling the value preset memory if the comparator of the franking machine has established that both individual information of the pair have been calculated according to the same rule. Thus, this rule forms an access code for the acquisition of new value quantities usable in the franking machine.
However, these known methods suffer from the disadvantage of a limited security against unauthorized value preset filling, because the code to the security system is valid for all the franking machines, i.e. the algorithm used as a basis for the calculation of authorizing numbers for all franking machines can be relatively easily determined by trial and error with the aid of conventional computers. The random number generators partly used in the known methods also contain a calculating rule and consequently do not supply true random numbers. Therefore, they also lead to limited security.